JP2021007121A - Organic electroluminescent element, display device, and lighting device - Google Patents

Abstract

To provide an organic electroluminescent element with high luminous efficacy and low driving voltage.SOLUTION: An organic electroluminescent element 1 comprises a positive electrode 3, a luminous layer 6 and a negative electrode 9 in this order. The luminous layer 6 contains a guest material and a host material. The host material is a compound represented by the general formula (1) in the figure, where X1 each independently represent N or C-R2, provided that at least one of the X1 is N.SELECTED DRAWING: Figure 1

Description

The present invention relates to an organic electroluminescence (hereinafter, electroluminescence (electric field emission) may be referred to as "EL") element, a display device, and a lighting device.

Organic EL elements are self-luminous, have a wide viewing angle, have excellent visibility, can be driven at a low voltage, can be made thinner and lighter by surface emission, and can display in multiple colors. doing. Therefore, the organic EL element can be suitably used for a display device such as a display or a lighting device.

An organic EL element is usually configured by laminating an anode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and a cathode in this order on a transparent substrate. The light emission of the organic EL element is generated through the steps (i) to (v) shown below.
(I) Holes and electrons are injected from the electrodes.
(Ii) The injected holes and electrons are transported.
(Iii) Holes and electrons recombine in the light emitting layer.
(Iv) The luminescent material forms an electronically excited state.
(V) The light emitting material emits light from an electronically excited state.

In an organic EL device, it has been proposed to use a phosphorescent material as a light emitting material of a light emitting layer in order to improve efficiency. When the luminescent material gains energy and becomes an electronically excited state, it generates a singlet excited state (S ₁ ) and a triplet excited state (T ₁ ) with a probability of 1: 3. Then, when the luminescent material returns from the electronically excited state to the ground state, it emits energy as light.

When a fluorescent material is used as the light emitting material, only the energy from S ₁ is converted into light. On the other hand, when a phosphorescent material is used as the light emitting material, not only the energy from S ₁ but also the energy from T ₁ is converted into light. Therefore, higher efficiency can be expected in the organic EL element using the phosphorescent material than in the organic EL element using the fluorescent material as the light emitting material (see, for example, Non-Patent Document 1 and Non-Patent Document 2). ).

Phosphorescent materials are typically used with host materials as guest materials. In an organic EL device having a light emitting layer containing a host material and a phosphorescent material (guest material), the energy of the host material excited by the recombination of holes and electrons is transferred to the phosphorescent material. The phosphorescent material is excited by the energy and emitted as light energy. In order to enable efficient energy transfer from the host material to the phosphorescent material, the energy of the triple term excited state (T ₁ ) of the host material is made larger than the T ₁ energy of the phosphorescent material which is the guest material. (See, for example, Non-Patent Document 3). If the T ₁ energy of the guest material is larger than the T ₁ energy of the host material, reverse energy transfer from the guest material to the host material may occur, which may hinder the high efficiency of phosphorescence emission.

Many host materials used for the light emitting layer have been reported so far. For example, a carbazole-based compound or the like can be mentioned as a host material, and the carbazole-based compound has a relatively large T ₁ energy.

As a light emitting material (guest material) for an organic EL device, an iridium complex capable of obtaining high external quantum efficiency is generally used. However, an organic EL device using an iridium complex as a light emitting material has a wide half width of the light emitting spectrum and low color purity. Therefore, in an organic EL device using an iridium complex as a light emitting material, it is necessary to sharpen the light emitting spectrum by using a color filter or the like, and the light utilization efficiency is low.

In recent years, as an organic EL element used for a display, a device that emits high color purity is required. For example, in ultra-high definition television (UHDTV), it is stipulated in ITU-R Recommendation BT.2020 to use a wide color gamut color system in which the three primary colors are located on the spectral locus (for example, non-patent). Reference 4).

Against this background, luminescent materials having a narrow half-value width of the luminescence spectrum are being developed. For example, Non-Patent Document 5 below describes a platinum complex having a specific structure as a light emitting material (guest material), and according to the platinum complex, a high color purity green having a half width of the emission spectrum of 18 nm. Luminescence is obtained.

However, when a material having a 1,3,5-triazine group is used as the host material of the light emitting layer to be combined with the platinum complex, an exciplex is likely to be formed between the host material and the light emitting material (guest material). It has been reported that the half width of the emission spectrum of an organic EL device is widened and the color purity is lowered (see, for example, Non-Patent Document 6).

Organic EL display, Ohmsha Co., Ltd., pp. 83 (2011) Org. Electron, 14, 260 (2013) Apple. Phys. Lett. , 83,569 (2003) Recognition ITU-R BT. 2020-2 (2015) t. Freesome, Arizona State University, PhD thesis, pp. 116-122 (2014) Molecules, 24,454 (2019)

In an organic EL element, it is required to lower the drive voltage while ensuring the luminous efficiency. However, in the conventional organic EL device, since the energy barrier in the movement of holes and electrons from the electrode to the light emitting layer is large, it is difficult to realize an device showing high external quantum efficiency while sufficiently lowering the drive voltage. ..
Further, in the conventional organic EL device, when a light emitting material (guest material) capable of high color purity light emission is used, it is difficult to obtain an element having high external quantum efficiency, low power consumption, and high color purity light emission. was.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an organic EL device having high luminous efficiency (high external quantum efficiency) and low drive voltage (low power consumption).
Further, the present invention further provides an organic EL element having high luminous efficiency, low driving voltage, and high color purity of emission when a light emitting material (guest material) capable of emitting high color purity is used. To be an issue.

As a result of diligent studies to solve the above problems, the present inventors have the following general formula in which the light emitting layer located between the two electrodes of the organic EL element contributes to hole transportability and electron transportability. By including the compound shown in (1), the energy barrier in the movement of holes and electrons to the light emitting layer becomes small, so that the driving voltage can be lowered, and the organic EL element having high light emitting efficiency and low driving voltage can be used. We found that it could be realized and came up with the present invention.
In addition, as a result of further diligent studies, the present inventors used a compound represented by the following general formula (1) as a host material for the light emitting layer, and used a planar tetradentate on a metal having a coordination number of 4 as a guest material. It has been found that an organic EL element having high emission efficiency, low driving voltage, and high emission color purity can be realized by using a complex to which a ligand is bonded.
The gist structure of the present invention for solving the above problems is as follows.

［一般式（１）中のＸ¹は、それぞれ独立にＮ又はＣ−Ｒ²を示し、少なくとも１つのＸ¹はＮであり、ここで、Ｒ²は、水素原子、炭素数１〜１０のアルキル基、炭素数１〜１０のアルコキシ基、炭素数１〜１０のアルキルチオ基、炭素数１〜１０のアルキルアミノ基、炭素数２〜１０のアシル基、炭素数７〜２０のアラルキル基、置換若しくは未置換の炭素数６〜３０の芳香族炭化水素基、又は置換若しくは未置換の炭素数３〜３０の芳香族複素環基であり、
Ｒ¹は、それぞれ独立に水素原子、炭素数１〜１０のアルキル基、炭素数１〜１０のアルコキシ基、炭素数１〜１０のアルキルチオ基、炭素数１〜１０のアルキルアミノ基、炭素数２〜１０のアシル基、炭素数７〜２０のアラルキル基、置換若しくは未置換の炭素数６〜３０の芳香族炭化水素基、又は置換若しくは未置換の炭素数３〜３０の芳香族複素環基であり、隣り合うＲ¹は一体となって環を形成していてもよい。］で表わされる化合物であることを特徴とする。
かかる本発明の有機エレクトロルミネッセンス素子は、発光効率が高く、駆動電圧が低い。 The organic electroluminescence element of the present invention includes an anode, a light emitting layer, and a cathode in this order.
The light emitting layer contains a guest material and a host material.
The host material is the following general formula (1):

[X ¹ in the general formula (1) independently represents N or C-R ² , and at least one X ¹ is N, where R ² is a hydrogen atom and has 1 to 10 carbon atoms. Alkyl group, alkoxy group with 1 to 10 carbon atoms, alkylthio group with 1 to 10 carbon atoms, alkylamino group with 1 to 10 carbon atoms, acyl group with 2 to 10 carbon atoms, aralkyl group with 7 to 20 carbon atoms, substitution Alternatively, it is an unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or an substituted or unsubstituted aromatic heterocyclic group having 3 to 30 carbon atoms.
R ¹ is independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, and 2 carbon atoms. An acyl group of 10 to 10, an aralkyl group having 7 to 20 carbon atoms, an aromatic hydrocarbon group having 6 to 30 substituted or unsubstituted carbon atoms, or an aromatic heterocyclic group having 3 to 30 carbon atoms substituted or unsubstituted. There, adjacent R ¹ may form a ring together. ] Is a compound represented by.
The organic electroluminescence element of the present invention has high luminous efficiency and low drive voltage.

In a preferred example of the organic electroluminescence device of the present invention, the guest material in the light emitting layer is an organometallic complex. In this case, the luminous efficiency is further increased.

［一般式（２）中のＸ¹は、それぞれ独立にＮ又はＣ−Ｒ²を示し、少なくとも１つのＸ¹はＮであり、ここで、Ｒ²は、水素原子、炭素数１〜１０のアルキル基、炭素数１〜１０のアルコキシ基、炭素数１〜１０のアルキルチオ基、炭素数１〜１０のアルキルアミノ基、炭素数２〜１０のアシル基、炭素数７〜２０のアラルキル基、置換若しくは未置換の炭素数６〜３０の芳香族炭化水素基、又は置換若しくは未置換の炭素数３〜３０の芳香族複素環基であり、
Ｒ¹は、それぞれ独立に水素原子、炭素数１〜１０のアルキル基、炭素数１〜１０のアルコキシ基、炭素数１〜１０のアルキルチオ基、炭素数１〜１０のアルキルアミノ基、炭素数２〜１０のアシル基、炭素数７〜２０のアラルキル基、置換若しくは未置換の炭素数６〜３０の芳香族炭化水素基、又は置換若しくは未置換の炭素数３〜３０の芳香族複素環基であり、隣り合うＲ¹は一体となって環を形成していてもよく、
Ｒ³は、それぞれ独立に水素原子、炭素数１〜１０のアルキル基、炭素数１〜１０のアルコキシ基、炭素数１〜１０のアルキルチオ基、炭素数１〜１０のアルキルアミノ基、炭素数２〜１０のアシル基、炭素数７〜２０のアラルキル基、置換若しくは未置換の炭素数６〜３０の芳香族炭化水素基、又は置換若しくは未置換の炭素数３〜３０の芳香族複素環基である。］で示される化合物である。この場合、発光効率が更に高くなり、駆動電圧が更に低くなる。 In another preferred example of the organic electroluminescence device of the present invention, the host material in the light emitting layer is the following general formula (2):

[X ¹ in the general formula (2) independently represents N or C-R ² , and at least one X ¹ is N, where R ² is a hydrogen atom and has 1 to 10 carbon atoms. Alkyl group, alkoxy group with 1 to 10 carbon atoms, alkylthio group with 1 to 10 carbon atoms, alkylamino group with 1 to 10 carbon atoms, acyl group with 2 to 10 carbon atoms, aralkyl group with 7 to 20 carbon atoms, substitution Alternatively, it is an unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or an substituted or unsubstituted aromatic heterocyclic group having 3 to 30 carbon atoms.
R ¹ is independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, and 2 carbon atoms. An acyl group of 10 to 10, an aralkyl group having 7 to 20 carbon atoms, an aromatic hydrocarbon group having 6 to 30 substituted or unsubstituted carbon atoms, or an aromatic heterocyclic group having 3 to 30 carbon atoms substituted or unsubstituted. There, adjacent R ¹ may form a ring together,
R ³ is independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, and 2 carbon atoms. An acyl group of 10 to 10, an aralkyl group having 7 to 20 carbon atoms, an aromatic hydrocarbon group having 6 to 30 substituted or unsubstituted carbon atoms, or an aromatic heterocyclic group having 3 to 30 carbon atoms substituted or unsubstituted. is there. ] Is a compound indicated by. In this case, the luminous efficiency becomes higher and the drive voltage becomes lower.

Further, it is preferable that the organometallic complex is a complex in which a planar tetradentate ligand is bonded to a metal having a coordination number of 4. In this case, it is possible to obtain an organic EL element having high luminous efficiency, low driving voltage, and high color purity of emission.

［一般式（３）中のＭは、配位数が４の金属であり、
Ｒ⁴、Ｒ⁵、Ｒ⁶、Ｒ⁷は、それぞれ、置換されていてもよい炭素環基又は置換されていてもよい複素環基であり、
Ｌ¹は、Ｒ⁴とＲ⁵とを連結する連結基であり、
Ｌ²は、Ｒ⁵とＲ⁶とを連結する連結基であり、
Ｌ³は、Ｒ⁶とＲ⁷とを連結する連結基である。］で示される化合物であることが更に好ましい。この場合、発光の色純度が更に高くなる。 Here, the complex has the following general formula (3):

[M in the general formula (3) is a metal having a coordination number of 4,
R ⁴ , R ⁵ , R ⁶ , and R ⁷ are optionally substituted carbocyclic groups or optionally substituted heterocyclic groups, respectively.
L ¹ is a linking group that connects R ⁴ and R ⁵ .
L ² is a linking group that connects R ⁵ and R ⁶ and
L ³ is a linking group that connects R ⁶ and R ⁷ . ] Is more preferable. In this case, the color purity of the emitted light becomes even higher.

で示されるいずれかの化合物であることがより一層好ましい。この場合、発光の色純度が更に高くなる。 In addition, the compounds represented by the general formula (3) have the following structural formulas (3-1) to (3-15):

It is even more preferable that it is any compound represented by. In this case, the color purity of the emitted light becomes even higher.

Further, it is particularly preferable that the guest material in the light emitting layer is a compound represented by the structural formula (3-1) or (3-3). In this case, the color purity of the emitted light becomes particularly high.

で示される化合物であることも好ましい。この場合、発光効率が更に高くなり、駆動電圧が更に低くなる。 Further, the organometallic complex has the following structural formula (4-1):

It is also preferable that it is a compound represented by. In this case, the luminous efficiency becomes higher and the drive voltage becomes lower.

Further, the display device of the present invention is characterized by including the above-mentioned organic electroluminescence element. The display device of the present invention has a low drive voltage and excellent luminous efficiency.

Further, the lighting device of the present invention is characterized by including the above-mentioned organic electroluminescence element. The lighting device of the present invention has a low drive voltage and excellent luminous efficiency.

According to the present invention, it is possible to provide an organic EL device in which a light emitting layer located between two electrodes contains the compound represented by the above general formula (1), has high luminous efficiency, and has a low drive voltage.
Further, according to a preferred embodiment of the present invention, the light emitting layer contains a compound represented by the above general formula (1) and a complex in which a planar tetradentate ligand is bonded to a metal having a coordination number of 4. It is possible to provide an organic EL element having high luminous efficiency, low driving voltage, and high emission color purity.

It is sectional drawing for demonstrating an example of the organic EL element of this embodiment. It is a graph which showed the result of having measured the emission spectrum at 300K and 77K of the thin film formed in Experiment 1. It is a graph which showed the result of having measured the emission spectrum at 300K and 77K of the thin film formed in Experiment 2. It is a graph which showed the relationship between the applied voltage and the brightness in the organic EL element of Example 1 and Comparative Example 1. It is a graph which showed the relationship between the current density and the power efficiency in the organic EL element of Example 1 and Comparative Example 1. It is a graph which shows the emission spectrum in the thin film formed in Experiment 4 and Experiment 5. It is a graph which showed the relationship between the applied voltage and the brightness in the organic EL element of Example 2 and Comparative Example 2. It is a graph which showed the relationship between the current density and the power efficiency in the organic EL element of Example 2 and Comparative Example 2.

Hereinafter, the organic electroluminescence device, the display device, and the lighting device of the present invention will be described in detail by way of examples based on the embodiments thereof.

<Organic electroluminescence element>
The organic electroluminescence element of the present invention includes an anode, a light emitting layer, and a cathode in this order, the light emitting layer includes a guest material and a host material, and the host material is the above general formula (1). ) Is a compound represented by).

で示される４，４’−ビス（９−カルバゾリル）−２，２’−ビフェニル（ＣＢＰ）が最も一般に用いられている。ＣＢＰは、正孔輸送性のみを示し、Ｓ₁（一重項励起状態）エネルギーとＴ₁（三重項励起状態）エネルギーとの差が大きい材料であり、エネルギーギャップが大きい。このため、ＣＢＰを用いた発光層を有する従来の有機ＥＬ素子では、電極から発光層への正孔及び電子の移動におけるエネルギー障壁が大きく、駆動電圧が高かった。
ここで、駆動電圧を低くするには、発光層のホスト材料として、ＣＢＰを用いた場合と同程度のＴ₁エネルギーを有し、ＣＢＰと比較してＳ₁エネルギーとＴ₁エネルギーとの差が小さい化合物を用いればよい。このことにより、ＣＢＰと比較してホスト材料のエネルギーギャップを小さくできる。
そこで、本発明者らは鋭意検討を重ね、発光層のホスト材料として、上記一般式（１）で示される化合物を用いればよいことを見出した。一般式（１）で示される化合物においては、ジヒドロアクリジン骨格又はジヒドロアントラセン骨格が正孔輸送性に寄与し、フェナントロイミダゾール骨格が電子輸送性に寄与する。このため、一般式（１）で示される化合物は、正孔輸送性と電子輸送性の両方を兼ね備え、Ｓ₁エネルギーとＴ₁エネルギーとの差が小さい。従って、一般式（１）で示される化合物をホスト材料として含む発光層を有する有機ＥＬ素子では、ホスト材料のエネルギーギャップが小さくなる。その結果、電極から発光層への正孔移動及び／又は電極から発光層への電子移動におけるエネルギー障壁が小さくなり、有機ＥＬ素子の駆動電圧が低くなる。しかも、一般式（１）で示される化合物をホスト材料として含む発光層を有する有機ＥＬ素子では、ホスト材料としてＣＢＰを用いた場合と同等の高い発光効率が得られる。
従って、発光層が、ホスト材料として、上記一般式（１）で表わされる化合物を含む本発明の有機ＥＬ素子は、発光効率が高く、駆動電圧が低い。 As described above, in the conventional organic EL device, a carbazole-based compound is generally used as a host material for the light emitting layer, and among the carbazole-based compounds, the following structural formula (5):

4,4'-bis (9-carbazolyl) -2,2'-biphenyl (CBP) represented by is most commonly used. CBP is a material that exhibits only hole transportability and has a large difference between S ₁ (singlet excited state) energy and T ₁ (triplet excited state) energy, and has a large energy gap. Therefore, in the conventional organic EL device having a light emitting layer using CBP, the energy barrier in the movement of holes and electrons from the electrode to the light emitting layer is large, and the driving voltage is high.
Here, in order to lower the drive voltage, the T ₁ energy is about the same as when CBP is used as the host material of the light emitting layer, and the difference between the S ₁ energy and the T ₁ energy is larger than that of the CBP. Smaller compounds may be used. This makes it possible to reduce the energy gap of the host material as compared to CBP.
Therefore, the present inventors have made extensive studies and found that the compound represented by the above general formula (1) may be used as the host material for the light emitting layer. In the compound represented by the general formula (1), the dihydroacridine skeleton or the dihydroanthracene skeleton contributes to the hole transport property, and the phenanthremidazole skeleton contributes to the electron transport property. Therefore, the compound represented by the general formula (1) has both hole transporting property and electron transporting property, and the difference between S ₁ energy and T ₁ energy is small. Therefore, in an organic EL device having a light emitting layer containing the compound represented by the general formula (1) as a host material, the energy gap of the host material becomes small. As a result, the energy barrier in the hole transfer from the electrode to the light emitting layer and / or the electron transfer from the electrode to the light emitting layer becomes small, and the driving voltage of the organic EL element becomes low. Moreover, in an organic EL device having a light emitting layer containing the compound represented by the general formula (1) as a host material, high luminous efficiency equivalent to that when CBP is used as the host material can be obtained.
Therefore, the organic EL device of the present invention in which the light emitting layer contains the compound represented by the above general formula (1) as a host material has high luminous efficiency and low driving voltage.

Next, one aspect of the organic electroluminescence device of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view for explaining an example of the organic EL element of the present embodiment.

In the organic EL element 1 of the present embodiment shown in FIG. 1, an anode 3, a light emitting layer 6, and a cathode 9 are provided in this order on a substrate 2, and the anode 3 (electrode) and the cathode 9 (electrode) are provided in this order. ), A laminated structure including the light emitting layer 6 is formed.
In the laminated structure of the organic EL element 1 of the present embodiment, the hole injection layer 4, the hole transport layer 5, the light emitting layer 6, the electron transport layer 7, and the electron injection layer 8 are formed in this order. It is a thing.
The organic EL element 1 shown in FIG. 1 may be a top-emission type that extracts light on the side opposite to the substrate 2, or may be a bottom-emission type that extracts light on the substrate 2 side.

(substrate)
Examples of the material of the substrate 2 include a resin material and a glass material. As the material of the substrate 2, only one kind may be used, or two or more kinds may be used in combination.
Examples of the resin material used for the substrate 2 include polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyarylate and the like. When a resin material is used as the material of the substrate 2, the organic EL element 1 having excellent flexibility can be obtained, which is preferable.
On the other hand, examples of the glass material used for the substrate 2 include quartz glass, soda glass, and Pyrex (registered trademark).

When the organic EL element 1 is a bottom emission type, a transparent substrate is used as the material of the substrate 2.
On the other hand, when the organic EL element 1 is a top emission type, not only a transparent substrate but also an opaque substrate may be used as the material of the substrate 2. Examples of the opaque substrate include a substrate made of a ceramic material such as alumina, a substrate having an oxide film (insulating film) formed on the surface of a metal plate such as stainless steel, and a substrate made of a resin material.

(anode)
The anode 3 injects holes into the hole injection layer 4 or the hole transport layer 5. Therefore, as the material of the anode 3, various metal materials having a relatively large work function, various alloys, and the like are used. Examples of the material of the anode 3 include gold, copper iodide, tin oxide, aluminum-doped zinc oxide (ZnO: Al), indium tin oxide (ITO), indium zinc oxide (IZO), tin fluorine oxide (FTO), and the like. Can be mentioned. Among these, ITO, IZO, and FTO are preferable as the material of the anode 3 from the viewpoint of transparency and work function.

When the organic EL element 1 is of the bottom emission type, a transparent conductive material is used as the material of the anode 3.
On the other hand, when the organic EL element 1 is of the top emission type, as the material of the anode 3, not only a transparent conductive material but also an opaque material may be used, or a reflective material may be used.

(Hole injection layer)
The material used for the hole injection layer 4 is selected according to the relationship between the work function of the anode 3 and the ionization potential (IP) of the hole transport layer 5, the charge transport characteristics, and the like. The material of the hole injection layer 4 may be any compound having appropriate IP and charge transport characteristics, and various organic compounds and inorganic compounds can be selected and used regardless of whether they are small molecules or polymers. The material of the hole injection layer 4 may be only one type, or two or more types may be used in combination.

Examples of the inorganic compound used in the hole injection layer 4 include molybdenum oxide (MoOx) and vanadium oxide (V ₂ O ₅ ). Inorganic compounds are more stable than organic compounds. Therefore, when an inorganic compound is used for the hole injection layer 4, high resistance to oxygen and water can be easily obtained as compared with the case where an organic compound is used.

Examples of the organic compound used in the hole injection layer 4 include compounds represented by the following structural formulas (6-1) to (6-19).

Among the compounds represented by the above structural formulas (6-1) to (6-19), the poly (3,4-ethylenedioxythiophene) represented by the structural formula (6-11): poly (styrene sulfonate) (PEDOT). : PSS), poly (3,4-ethylenedioxythiophene) (PEDOT) represented by the structural formula (6-12), and copper phthalocyanine (CuPc) represented by the structural formula (6-4) are preferable. PEDOT shown in 6-12) is particularly preferable.

(Hole transport layer)
Examples of the material used for the hole transport layer 5 include compounds represented by the following structural formulas (7-1) to (7-37).

Among the compounds represented by the above structural formulas (7-1) to (7-37), N, N'-di (1-naphthyl) -N, N'-diphenyl- represented by the structural formula (7-1). With 1,1'-biphenyl-4,4'-diamine (α-NPD) and structural formula (7-36) or (7-37) with a large band gap and excellent electrical and thermal stability. It is particularly preferred to use in combination with the compounds shown.

The material of the hole transport layer 5 may be only one type, or two or more types may be used in combination. Further, the hole transport layer 5 may be formed by only one layer, or may be formed by stacking two or more layers. For example, the hole transport layer 5 has a layer composed of the compound represented by the structural formula (7-36) or (7-37) arranged on the light emitting layer 6 side and a structural formula (7-37) arranged on the hole injection layer 4 side. The layer made of α-NPD represented by 7-1) can be laminated.

(Light emitting layer)
The light emitting layer 6 included in the organic EL element 1 of the present embodiment includes a host material that performs charge transport and charge recombination, and a guest material that is a light emitting material.

で表わされる化合物を用いる。
一般式（１）で示される化合物中のジヒドロアクリジン骨格又はジヒドロアントラセン骨格は、正孔輸送性に寄与するドナー性を有する。また、一般式（１）で示される化合物中のフェナントロイミダゾール骨格は、電子輸送性に寄与するアクセプター性の置換基である。 "Host material"
In the present embodiment, as the host material, the following general formula (1):

The compound represented by is used.
The dihydroacridine skeleton or dihydroanthracene skeleton in the compound represented by the general formula (1) has a donor property that contributes to hole transportability. The phenanthroimidazole skeleton in the compound represented by the general formula (1) is an acceptor-type substituent that contributes to electron transport.

X ¹ in the general formula (1) independently represents N or CR ² , and at least one X ¹ is N. Here, R ² is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, and 2 carbon atoms. An acyl group of 10 to 10, an aralkyl group having 7 to 20 carbon atoms, an aromatic hydrocarbon group having 6 to 30 substituted or unsubstituted carbon atoms, or an aromatic heterocyclic group having 3 to 30 carbon atoms substituted or unsubstituted. is there.

R ¹ in the general formula (1) has a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, and 1 to 10 carbon atoms, respectively. Alkylamino groups, acyl groups with 2 to 10 carbon atoms, aralkyl groups with 7 to 20 carbon atoms, aromatic hydrocarbon groups with 6 to 30 substituted or unsubstituted carbon atoms, or substituted or unsubstituted aromatic hydrocarbon groups with 3 to 30 carbon atoms. an aromatic heterocyclic group, adjacent R ¹ may form a ring together.
Here, "adjacent R ^1" is the same two R ¹ attached to a carbon atom, and R ¹ attached to each of the two carbon atoms to which they are attached is the inclusion ..

で示される化合物が好ましい。この場合、発光効率が更に高くなり、駆動電圧が更に低くなる。 Examples of the compound represented by the general formula (1) include the following general formula (2):

The compound represented by is preferable. In this case, the luminous efficiency becomes higher and the drive voltage becomes lower.

X ¹ in the general formula (2) independently represents N or CR ² , and at least one X ¹ is N. Here, R ² is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, and 2 carbon atoms. An acyl group of 10 to 10, an aralkyl group having 7 to 20 carbon atoms, an aromatic hydrocarbon group having 6 to 30 substituted or unsubstituted carbon atoms, or an aromatic heterocyclic group having 3 to 30 carbon atoms substituted or unsubstituted. is there.

R ¹ in the general formula (2) has a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, and 1 to 10 carbon atoms, respectively. Alkylamino groups, acyl groups with 2 to 10 carbon atoms, aralkyl groups with 7 to 20 carbon atoms, aromatic hydrocarbon groups with 6 to 30 substituted or unsubstituted carbon atoms, or substituted or unsubstituted aromatic hydrocarbon groups with 3 to 30 carbon atoms. an aromatic heterocyclic group, adjacent R ¹ may form a ring together.
Here, "adjacent R ^1" is the same two R ¹ attached to a carbon atom, and R ¹ attached to each of the two carbon atoms to which they are attached is the inclusion ..

R ³ in the general formula (2) has a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, and 1 to 10 carbon atoms, respectively. Alkylamino group, acyl group with 2 to 10 carbon atoms, aralkyl group with 7 to 20 carbon atoms, aromatic hydrocarbon group with 6 to 30 carbon atoms substituted or unsubstituted, or 3 to 30 carbon atoms substituted or unsubstituted It is an aromatic heterocyclic group of.

Regarding R ¹ , R ² , and R ³ described above, the alkyl groups having 1 to 10 carbon atoms include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, and nonyl group. Examples of the alkoxy group having 1 to 10 carbon atoms include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group, a tert-butoxy group, a pentyloxy group, a hexyloxy group and a heptyloxy group. Examples of the alkylthio group having 1 to 10 carbon atoms include a methylthio group, an ethylthio group, a propylthio group, a butylthio group, a pentylthio group, a hexylthio group, a heptylthio group, an octylthio group, a nonylthio group and the like. Examples of the alkylamino group having 1 to 10 carbon atoms include a methylamino group, an ethylamino group, a propylamino group, a butylamino group, a pentylamino group, a hexylamino group, a heptylamino group, an octylamino group and a nonylamino group. Examples of the acyl group having 2 to 10 carbon atoms include an acetyl group, a propionyl group and a butyryl group, and examples of the aralkyl group having 7 to 20 carbon atoms include a benzyl group, a phenethyl group, a phenylpropyl group and a naphthyl group. Examples of the substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms include a methyl group, a phenyl group, a 2,6-xysilyl group, a mesityl group, a duryl group, a biphenyl group, a terphenyl group, and a naphthyl. Examples thereof include a group, anthryl group, pyrenyl group, toluyl group, anisyl group, fluorophenyl group, diphenylaminophenyl group, dimethylaminophenyl group, diethylaminophenyl group, pyridylphenyl group, phenanthrenyl group and the like, and the number of substituted or unsubstituted carbon atoms. Examples of the aromatic heterocyclic group of 3 to 30 include a pyridyl group, a pyrazinyl group, a pyrimidinyl group, a pyridadinyl group, a triazine group and the like.

で示される化合物が特に好ましい。上記構造式（１−１）又は（１−２）で示される化合物は、一重項励起状態（Ｓ₁）と三重項励起状態（Ｔ₁）とのエネルギー差が小さく、且つエネルギーギャップが小さいため、外部量子効率が高い有機ＥＬ素子１が得られ易く、好ましい。 Examples of the compound represented by the general formula (1) include the following structural formulas (1-1) or (1-2):

The compound represented by is particularly preferable. The compound represented by the structural formula (1-1) or (1-2) has a small energy difference between the singlet excited state (S ₁ ) and the triplet excited state (T ₁ ), and the energy gap is small. It is preferable that the organic EL element 1 having high external quantum efficiency can be easily obtained.

By measuring the fluorescence spectrum of the compound, the S ₁ (single term excited state) energy of the compound can be obtained. Further, the T ₁ (triplet excited state) energy of the compound can be obtained by measuring the phosphorescence spectrum of the compound.

The compound represented by the general formula (1) can be obtained by synthesizing by a known method. The method for synthesizing the compound represented by the general formula (1) is not particularly limited, but for example, a dihydroacridine compound or a dihydroanthracene compound is coupled with a phenanthreimidazole compound having a bromophenyl group. Can be synthesized by. Here, a compound having a desired structure can be appropriately synthesized by introducing a desired substituent into a dihydroacridine compound or a dihydroanthracene compound, and / or a phenanthremidazole compound having a bromophenyl group.

"Guest material"
As the guest material, it is preferable to use a fluorescent material and / or a phosphorescent material. The guest material preferably has an absorption wavelength that overlaps the emission wavelength of the host material in order to effectively transfer energy from the host material.
The content of the guest material in the host material is preferably 1 to 10% by mass. When the content of the guest material is in the above range, energy transfer from the host material to the guest material occurs efficiently, and the luminous efficiency of the organic EL element 1 becomes good.

-Phosphorescent material-
If the guest material is a phosphorescent material, the T ₁ energy of the guest material is preferably smaller than the T ₁ energy of the host material.
Examples of the phosphorescent material used as the guest material include compounds represented by the following structural formulas (4-1) to (4-29).

In the present embodiment, since the compound represented by the general formula (1) is used as the host material, the structural formula (4) is among the phosphorescent materials represented by the structural formulas (4-1) to (4-29). A green light emitting material such as Ir (mppy) ₃ represented by -1) is particularly preferable.

Since Ir (mppy) ₃ represented by the above structural formula (4-1) has a relatively small T ₁ energy, a compound represented by the general formula (1) is used as the host material, and Ir (mppy) ₃ is used as the guest material. When is used, efficient energy transfer from the host material to the guest material occurs. As a result, the organic EL element 1 has a lower drive voltage. Further, since Ir (mppy) ₃ has an absorption wavelength that overlaps with the emission wavelength of the compound represented by the general formula (1), it becomes an organic EL element 1 having higher luminous efficiency.

When a compound represented by the general formula (1) is used as the host material and Ir (mppy) ₃ is used as the guest material, the content of the guest material in the host material is preferably 1 to 6% by mass. When the content of the guest material is within the above range, energy transfer from the host material to the guest material occurs efficiently, and the efficiency decrease due to triplet-triplet annihilation (TTA) due to the increase in the guest material concentration can be prevented. it can. Therefore, the luminous efficiency of the organic EL element 1 becomes good.

-Fluorescent material-
Examples of the fluorescent material used as the guest material include compounds represented by the following structural formulas (4-30) to (4-51).

-Organometallic complex-
As the guest material in the light emitting layer 6, it is preferable to use an organometallic complex. When an organometallic complex is used as the guest material, the luminous efficiency is further increased.
Examples of the organometallic complex include phosphorescent materials represented by the structural formulas (4-1) to (4-29) described above, and a planar tetradentate ligand on a metal having a coordination number of 4, which will be described later. Examples thereof include bonded complexes.

The guest material in the light emitting layer 6 preferably contains a complex in which a planar tetradentate ligand is bound to a metal having a coordination number of 4 from the viewpoint of obtaining light emission with high color purity. Luminous efficiency is improved by using the compound represented by the above general formula (1) as the host material of the light emitting layer 6 and using a complex in which a planar tetradentate ligand is bonded to a metal having a coordination number of 4 as a guest material. The organic EL element 1 having a high driving voltage, a low driving voltage, and a high luminous color purity can be obtained.
Since the compound represented by the general formula (1) has a small energy gap and a T ₁ energy larger than that of the guest material, a planar tetradentate ligand on a metal having a coordination number of 4 in the light emitting layer 6 High external quantum efficiency can be obtained by using it together with the complex to which is bonded.
Further, the compound represented by the general formula (1) has a phenanthreimidazole skeleton as a skeleton having electron transportability, and the phenanthroimidazole skeleton is different from the 1,3,5-triazine skeleton and is a guest. Even if a complex in which a planar tetradentate ligand is bonded to a metal having a coordination number of 4 is used as the material, the formation of an exciplex between the host material and the guest material as described in Non-Patent Document 6 can be suppressed. .. Therefore, by using the compound represented by the general formula (1) as the host material and using a complex in which a planar tetradentate ligand is bonded to a metal having a coordination number of 4 as the guest material, the half width of the emission spectrum can be increased. It is narrow and emits high color purity.

で示される化合物が好ましい。
上記一般式（３）で示される化合物は、四座配位子が、金属を囲むように略同一平面上に配置された４つの環状構造を有する基と、隣接する環状構造を有する基の間のうちの３箇所をそれぞれ連結する連結基とを有する。このため、一般式（３）で示される化合物は、安定であり、分子の振動に伴う光の放射が効果的に抑制され、発光スペクトルの半値幅が狭く、高色純度の発光が得られるものと推定される。 The complex in which a planar tetradentate ligand is bonded to a metal having a coordination number of 4 may contain only one type, or may contain two or more types. As a complex in which a planar tetradentate ligand is bonded to a metal having a coordination number of 4, the following general formula (3):

The compound represented by is preferable.
In the compound represented by the general formula (3), the tetradentate ligand is between a group having four cyclic structures arranged on substantially the same plane so as to surround the metal and a group having an adjacent cyclic structure. It has a linking group that connects each of the three locations. Therefore, the compound represented by the general formula (3) is stable, the radiation of light accompanying the vibration of the molecule is effectively suppressed, the half width of the emission spectrum is narrow, and the emission of high color purity can be obtained. It is estimated to be.

M in the general formula (3) is a metal having a coordination number of 4. M in the general formula (3) may be a metal having a coordination number of 4, and examples thereof include Pt, Pd, and Cu, with Pt and Pd being preferable, and Pt being particularly preferable.

R ⁴ , R ⁵ , R ⁶ and R ⁷ in the general formula (3) are a carbocyclic group which may be substituted or a heterocyclic group which may be substituted, respectively. The carbon ring group or heterocyclic group as R ⁴ , R ⁵ , R ⁶ , and R ⁷ is a 5-membered ring or a 6-membered ring because it is a compound that further suppresses the vibration of the molecule due to the radiation of light. Is preferable. R ⁴ , R ⁵ , R ⁶ , and R ⁷ in the general formula (3) may all be the same, or some or all may be different from each other.

Regarding R ⁴ , R ⁵ , R ⁶ and R ⁷ described above, the carbocyclic groups include cyclopentyl group, cyclohexyl group, phenyl group, biphenyl group, terphenyl group, naphthyl group, anthryl group, pyrenyl group and phenanthrenyl. Examples of the heterocyclic group include an imidazolyl group, a pyrazolyl group, a pyridyl group, a pyrazinyl group, a pyrimidinyl group, a pyridadinyl group, a benzoimidazolyl group, a carbazolyl group and the like. The substituents of the carbocyclic group and the heterocyclic group include an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, and an alkylamino having 1 to 10 carbon atoms. Examples thereof include a group and an acyl group having 2 to 10 carbon atoms.

L ¹ in the general formula (3) is a connecting group that connects R ⁴ and R ⁵ , L ² is a connecting group that connects R ⁵ and R ⁶ , and L ³ is R ⁶ . It is a linking group that connects R ⁷ and R ⁷ . L ¹ , L ² , and L ³ in the general formula (3) may be any one that connects groups having an adjacent cyclic structure (R ⁴ , R ⁵ , R ⁶ , R ⁷ ), for example. It may be a ring structure formed with atoms forming a group having an adjacent cyclic structure, or it may be a single bond between atoms forming a group having an adjacent cyclic structure. It may be an ether bond. L ¹ , L ² , and L ³ in the general formula (3) may all be the same, or some or all may be different from each other.

As the compound represented by the general formula (3), the compounds represented by the following structural formulas (3-1) to (3-15) are preferable, and among these, the structural formula is easy to obtain high color purity emission. The compound represented by (3-1) and the compound represented by the structural formula (3-3) are particularly preferable.

When the compound represented by the general formula (1) is used as the host material and the compound represented by the general formula (3) is used as the guest material, the content of the guest material in the host material is 3 to 10% by mass. Is preferable. When the content of the guest material is within the above range, energy transfer from the host material to the guest material occurs efficiently, and the efficiency decrease due to triplet-triplet annihilation (TTA) due to the increase in guest concentration can be prevented. .. Therefore, the luminous efficiency of the organic EL element 1 is further improved.

(Electronic transport layer)
When an electron transport layer 7 having an appropriate minimum unoccupied molecular orbital (LUMO) level is provided between the cathode 9 or the electron injection layer 8 and the light emitting layer 6, the cathode 9 or the electron injection layer 8 to the electron transport layer 7 are provided. The electron injection barrier to the light emitting layer 6 is relaxed, and the electron injection barrier from the electron transport layer 7 to the light emitting layer 6 is relaxed. Also, if the material used for the electron transport layer 7 has an appropriate highest occupied molecular orbital (HOMO) level, holes that flow out to the counter electrode without recombination in the light emitting layer 6 are blocked. As a result, holes are confined in the light emitting layer 6 and the recombination efficiency in the light emitting layer 6 is enhanced.
The electron transport layer 7 may be omitted if the electron injection barrier does not matter and the electron transport capacity of the light emitting layer 6 is sufficiently high.

Examples of the material used for the electron transport layer 7 include compounds represented by the following structural formulas (8-1) to (8-28).

Among the compounds represented by the above structural formulas (8-1) to (8-28), 2,2', 2 "-(1,3,5-benzenetriyl) represented by the structural formula (8-4). -Tris (1-phenyl-1-H-benzimidazole) (TPBi) is particularly preferred.

(Electron injection layer)
The material used for the electron injection layer 8 is selected from the viewpoint of the work function of the cathode 9 and the LUMO level of the electron transport layer 7. The material used for the electron injection layer 8 is selected in consideration of the LUMO level of the guest material and the host material of the light emitting layer 6 when the electron transport layer 7 is not provided.

The material used for the electron injection layer 8 may be an organic compound or an inorganic compound. When the electron injection layer 8 is made of an inorganic compound, for example, in addition to alkali metal and alkaline earth metal, lithium fluoride, sodium fluoride, potassium fluoride, cesium fluoride, cesium carbonate and the like can be used. It can be used, and it is preferable to use lithium fluoride.

(cathode)
The cathode 9 injects electrons into the electron injection layer 8 or the electron transport layer 7. Therefore, as the material of the cathode 9, various metal materials having a relatively small work function, various alloys, and the like are used. Examples of the material of the cathode 9 include aluminum, silver, magnesium, calcium, gold, indium tin oxide (ITO), indium zinc oxide (IZO), magnesium indium alloy (MgIn), silver alloy and the like.

When the organic EL element 1 is of the bottom emission type, an opaque electrode made of metal can be used as the material of the cathode 9, and a reflective material may be used.
On the other hand, when the organic EL element 1 is of the top emission type, a transparent conductive material is used as the material of the cathode 9. When ITO is used as the material of the cathode 9, electron injection becomes difficult because the work function of ITO is large. Further, since the ITO film is formed by using a sputtering method or an ion beam vapor deposition method, there is a possibility that the electron injection layer 8 or the like may be damaged during the film formation. Therefore, when ITO is used as the material of the cathode 9, it is preferable to provide a magnesium layer or a copper phthalocyanine layer between the electron injection layer 8 and the ITO.

(Formation method)
The organic EL element 1 shown in FIG. 1 has an anode 3, a hole injection layer 4, a hole transport layer 5, a light emitting layer 6, an electron transport layer 7, an electron injection layer 8, and an electron injection layer 8 on a substrate 2. It can be manufactured by forming the cathode 9 in this order. The method of forming each of the anode 3, the hole injection layer 4, the hole transport layer 5, the light emitting layer 6, the electron transport layer 7, the electron injection layer 8, and the cathode 9 is not particularly limited, and the characteristics of the material used for each layer are not particularly limited. It can be formed by appropriately using various conventionally known forming methods.

Specifically, for example, as a method for forming the anode 3 and the cathode 9, a sputtering method, a vacuum vapor deposition method, a sol-gel method, a spray pyrolysis (SPD) method, an atomic layer deposition (ALD) method, and a vapor phase deposition method , Liquid phase deposition method and the like.
Further, as a method of forming each layer of the hole injection layer 4, the hole transport layer 5, the light emitting layer 6, the electron transport layer 7, and the electron injection layer 8, a coating method in which an organic compound solution containing an organic compound to be each layer is applied is applied. Examples thereof include a method, a vacuum vapor deposition method, and an ESDUS (Evasorative Spray Depositionation from Ultra-dilute Solution) method. Among these forming methods, it is particularly preferable to use the coating method.
When any one of the hole injection layer 4, the hole transport layer 5, the electron transport layer 7, and the electron injection layer 8 is made of an inorganic material, the layer made of the inorganic material is, for example, a sputtering method. , Can be formed by using a method such as vacuum deposition.

(Other examples)
The organic EL device of the present invention is not limited to the organic EL device described in the above-described embodiment.
Specifically, in the above-described embodiment, the organic EL device 1 having a forward structure in which the anode 3 is arranged between the substrate 2 and the light emitting layer 6 has been described as an example, but the organic EL device of the present invention has been described. May have an inverted structure in which a cathode is arranged between the substrate and the light emitting layer.

Further, in the organic EL device of the present invention, the hole injection layer, the hole transport layer, the electron transport layer, and the electron injection layer may be formed as needed and may not be provided.
Further, each layer of the anode, the hole injection layer, the hole transport layer, the light emitting layer, the electron transport layer, the electron injection layer, and the cathode may be formed by one layer, or may be composed of two or more layers. It may be one.
Further, the organic EL device of the present invention may have another layer between each layer of the anode, the hole injection layer, the hole transport layer, the light emitting layer, the electron transport layer, the electron injection layer, and the cathode. Good. Specifically, an electron blocking layer or the like may be provided, if necessary, for the purpose of further improving the characteristics of the organic EL element.

<Display device>
The display device of the present invention is characterized by including the above-mentioned organic electroluminescence element. Since the display device of the present invention includes the above-mentioned organic EL element having high luminous efficiency and low driving voltage, the luminous efficiency is high and the driving voltage is low. In addition to the organic EL element described above, the display device of the present invention can include other parts generally used in the display device.

<Lighting device>
The lighting device of the present invention is characterized by including the above-mentioned organic electroluminescence element. Since the lighting device of the present invention includes the above-mentioned organic EL element having high luminous efficiency and low driving voltage, it has high luminous efficiency and low driving voltage. In addition to the organic EL element described above, the lighting device of the present invention can include other parts generally used in the lighting device.

Hereinafter, examples and comparative examples of the present invention will be described. The present invention is not limited to the examples shown below.

<Experiment 1>
A thin film having a thickness of 50 nm made of the compound represented by the following structural formula (1-1) was formed on a substrate made of a glass material by a vacuum vapor deposition method.

The compound represented by the structural formula (1-1) {2- (4- (9,9-diphenylacridine-10 (9H) -yl) phenyl) -1- (4-methoxyphenyl) -1H-phenanthro [ 9,10-d] imidazole (PhImEn)} Mater. Chem. C, 2018, 6, 9363-9377 was synthesized by the method described.

<Experiment 2>
A thin film having a thickness of 50 nm made of CBP represented by the above structural formula (5) was formed on a substrate made of a glass material by a vacuum vapor deposition method.

<Experiment 3>
A thin film having a thickness of 50 nm made of Ir (mppy) ₃ represented by the above structural formula (4-1) was formed on a substrate made of a glass material by a vacuum vapor deposition method.

(Measurement of emission spectrum)
For the thin film formed in Experiment 1, the emission spectra at 300K and 77K were measured using a FluoroMax-4 manufactured by HORIBA and an excitation light source having a wavelength of 300 nm. Further, for the thin film formed in Experiment 2, the emission spectra at 300K and 77K were measured using an excitation light source having a wavelength of 300 nm using the same apparatus. The results are shown in FIGS. 2 and 3. FIG. 2 is a graph showing the measurement results of the thin film formed in Experiment 1. FIG. 3 is a graph showing the measurement results of the thin film formed in Experiment 2.

The emission spectrum at room temperature (300K) shows fluorescence emission. Therefore, from the emission spectrum at room temperature (300K), the knowledge corresponding to the S ₁ (singlet excited state) energy can be obtained.
As shown in FIGS. 2 and 3, the fluorescent emission of the compound represented by the structural formula (1-1) (Experiment 1) is observed on the longer wavelength side than the fluorescent emission of CBP (Experiment 2). Therefore, the S ₁ energy of the compound represented by the structural formula (1-1) is smaller than that of CBP.

Further, with respect to the thin films formed in Experiments 1 and 2, phosphorescence emission was observed by measuring the emission spectrum at a low temperature (77K or less), and the energy of the triplet excited state (T ₁ ) of the thin films was determined. The emission spectrum was measured at a low temperature with a delay of 50 ms after the excitation light irradiation in order to remove the fluorescence emission component and observe the phosphorescence spectrum. Table 1 shows the energies of the triplet excited state (T ₁ ) of the thin films formed in Experiments 1 and 2 thus obtained.
Further, for the thin film (Ir (mppy) ₃ ) formed in Experiment 3, the energy of the triplet excited state (T ₁ ) of the thin film was obtained in the same manner as in Experiment 1 and Experiment 2. Table 1 shows the energy of the triplet excited state (T ₁ ) of the thin film formed in Experiment 3.

As described above, the S ₁ energy of the compound represented by the structural formula (1-1) is smaller than that of CBP. Further, as shown in Table 1, the T ₁ energy of the compound (Experiment 1) represented by the structural formula (1-1) is almost the same as that of CBP (Experiment 2). Therefore, the compound represented by the structural formula (1-1) has a smaller energy gap than CBP. Therefore, it can be seen that the compound represented by the structural formula (1-1) is preferable to CBP as a host material for the light emitting layer.

Further, as shown in Table 1, the T ₁ energy of the compound (Experiment 1) represented by the structural formula (1-1) is higher than the T ₁ energy of Ir (mppy) ₃ , which is a general green phosphorescent material. The compound, which is not small and is represented by the structural formula (1-1), is suitable as a host material for the light emitting layer.

<Example 1>
Using the materials shown below, the organic EL element of Example 1 was produced by the method shown below.
On the anode of the substrate, a hole injection layer, a second hole transport layer, a first hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and a cathode were formed by a vacuum deposition method. Was formed in this order to produce the organic EL element of Example 1.

(Substrate, anode)
A commercially available transparent glass substrate having an average thickness of 0.7 mm and having electrodes patterned to a width of 3 mm made of ITO (indium tin oxide).

(Hole injection layer)
PEDOT (Clevios HIL1.5) (thickness 30 nm) represented by the structural formula (6-12)

(Hole transport layer)
"First hole transport layer": Compound represented by structural formula (7-36) (thickness 10 nm)
"Second hole transport layer": α-NPD (thickness 20 nm) represented by the structural formula (7-1).

(Light emitting layer)
The compound represented by the structural formula (1-1), which is a compound represented by the general formula (1), is used as the host material, and Ir (mppy) represented by the structural formula (4-1), which is a guest material in the host material, is used. ) ₃ by mass% (thickness 25 nm)

(Electronic transport layer)
TPBi (thickness 35 nm) represented by the structural formula (8-4)

(Electron injection layer)
LiF film (thickness 0.8 nm)

(cathode)
Al film (thickness 100 nm)

<Comparative example 1>
An organic EL device of Comparative Example 1 was produced in the same manner as in Example 1 except that the compound used as the host material of the light emitting layer was CBP represented by the structural formula (5).

(Measurement of external quantum efficiency)
The external quantum efficiencies of the organic EL devices of Example 1 and Comparative Example 1 obtained as described above were measured at a current density of 10 mA / cm ² , respectively. The results are shown in Table 2.

As shown in Table 2, the external quantum efficiency of the organic EL device of Example 1 was higher than that of the external quantum efficiency of the organic EL device of Comparative Example 1.

(Measurement of voltage-luminance characteristics)
A voltage was applied to the organic EL elements of Example 1 and Comparative Example 1 using a "2400 type source meter" manufactured by Caseley, and the brightness was measured using "LS-100" manufactured by Konica Minolta. , The relationship between the applied voltage and the brightness was investigated. The results are shown in FIG.

As shown in FIG. 4, in the organic EL element of Example 1, higher brightness was obtained when the applied voltage was the same, and the drive voltage was lower than that of the organic EL element of Comparative Example 1. It is presumed that this is because the compound represented by the structural formula (1-1) used in Example 1 as the host material of the light emitting layer has a smaller energy gap than the CBP used in Comparative Example 1. Will be done.

(Measurement of current density-power efficiency characteristics)
The current density and power efficiency of the organic EL elements of Example 1 and Comparative Example 1 were examined using a "2400 type source meter" manufactured by Keithley. The results are shown in FIG.

As shown in FIG. 5, in the organic EL element of Example 1, higher power efficiency is obtained when the current densities are the same as compared with the organic EL element of Comparative Example 1. It is presumed that this is because the compound represented by the structural formula (1-1) used in Example 1 as the host material of the light emitting layer has a smaller energy gap than the CBP used in Comparative Example 1. Will be done.

<Experiment 4>
A thin film having a thickness of 30 nm containing 1% by mass of the compound represented by the structural formula (3-1) in the compound represented by the structural formula (1-1) was produced by vacuum vapor deposition on a quartz substrate.

で示される化合物を用いたこと以外は、実験４と同様にして、実験５の薄膜を作製した。 <Experiment 5>
Instead of the compound represented by the structural formula (1-1), the following structural formula (9):

A thin film of Experiment 5 was prepared in the same manner as in Experiment 4 except that the compound shown in (1) was used.

(Measurement of emission spectrum)
For the thin films obtained in Experiment 4 and Experiment 5, the emission spectrum at 300 K was measured using a FluoroMax-4 manufactured by HORIBA and an excitation light source having a wavelength of 350 nm. The results are shown in FIG.

As shown in FIG. 6, in the emission spectrum of the thin film of Experiment 4, it was confirmed that the emission intensity of the peak observed near 560 nm was smaller and the color purity of the emission was higher than that of the thin film of Experiment 5. Compared with the case where the compound represented by the structural formula (9) having a triazine group is used as the host material, it is better to use the compound represented by the structural formula (1-1) having a phenanthroimidazole group as the host. This is because the formation of an exciplex is unlikely to occur between the material and the guest material (the compound represented by the structural formula (3-1)), and the increase in the emission spectrum width due to this can be reduced.

<Example 2>
Using the materials shown below, the organic EL device of Example 2 was produced by the method shown below.
On the anode of the substrate, a hole injection layer, a second hole transport layer, a first hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and a cathode were formed by a vacuum deposition method. Was formed in this order to produce the organic EL element of Example 2.

(Substrate, anode)
A commercially available transparent glass substrate having an electrode (anode) patterned with a width of 3 mm made of ITO (indium tin oxide) and having an average thickness of 0.7 mm.

(Hole injection layer)
PEDOT (Clevios HIL1.3N) (thickness 30 nm) represented by the structural formula (6-12).

(Hole transport layer)
"First hole transport layer": Compound represented by structural formula (7-37) (thickness 10 nm)
"Second hole transport layer": α-NPD (thickness 20 nm) represented by the structural formula (7-1).

(Light emitting layer)
The compound represented by the structural formula (1-1) is used as the host material, and the host material contains 6% by mass of the compound represented by the structural formula (3-1) as the guest material (thickness 25 nm).

(Electronic transport layer)
TPBi (thickness 35 nm) represented by the structural formula (8-4)

(Electron injection layer)
LiF film (thickness 0.8 nm)

(cathode)
Al film (thickness 100 nm)

<Comparative example 2>
The organic EL device of Comparative Example 2 was produced in the same manner as in Example 2 except that the compound used as the host material of the light emitting layer was CBP represented by the structural formula (5).

(Measurement of external quantum efficiency)
For the organic EL devices of Example 2 and Comparative Example 2 obtained as described above, the external quantum efficiency at a current density of 10 mA / cm ² was measured by the same method as described above. The results are shown in Table 3.

As shown in Table 3, the external quantum efficiency of the organic EL element of Example 2 was higher than that of the external quantum efficiency of the organic EL element of Comparative Example 2.

(Measurement of voltage-luminance characteristics)
A voltage was applied to the organic EL elements of Example 2 and Comparative Example 2 using a "2400 type source meter" manufactured by Keithley, and the brightness was measured using "LS-100" manufactured by Konica Minolta. , The relationship between the applied voltage and the brightness was investigated. The results are shown in FIG.

As shown in FIG. 7, in the organic EL element of Example 2, higher brightness was obtained when the applied voltage was the same, and the drive voltage was lower than that of the organic EL element of Comparative Example 2.

(Measurement of current density-power efficiency characteristics)
The current density and power efficiency of the organic EL devices of Example 2 and Comparative Example 2 were examined by the same method as described above. The results are shown in FIG.

As shown in FIG. 8, even in the organic EL element of Example 2 in which the light emitting material (guest material) of Example 1 is changed, the current is compared with the organic EL element of Comparative Example 2 in which CBP is used as the host material. High power efficiency is obtained when the densities are the same.

1: Organic EL (electroluminescence) element 2: Substrate 3: Anode 4: Hole injection layer 5: Hole transport layer 6: Light emitting layer 7: Electron transport layer 8: Electron injection layer 9: Cathode

Claims (10)

The anode, the light emitting layer, and the cathode are provided in this order.
The light emitting layer contains a guest material and a host material.
The host material is the following general formula (1):

[X ¹ in the general formula (1) independently represents N or C-R ² , and at least one X ¹ is N, where R ² is a hydrogen atom and has 1 to 10 carbon atoms. Alkyl group, alkoxy group with 1 to 10 carbon atoms, alkylthio group with 1 to 10 carbon atoms, alkylamino group with 1 to 10 carbon atoms, acyl group with 2 to 10 carbon atoms, aralkyl group with 7 to 20 carbon atoms, substitution Alternatively, it is an unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or an substituted or unsubstituted aromatic heterocyclic group having 3 to 30 carbon atoms.
R ¹ is independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, and 2 carbon atoms. An acyl group of 10 to 10, an aralkyl group having 7 to 20 carbon atoms, an aromatic hydrocarbon group having 6 to 30 substituted or unsubstituted carbon atoms, or an aromatic heterocyclic group having 3 to 30 carbon atoms substituted or unsubstituted. There, adjacent R ¹ may form a ring together. ], Which is an organic electroluminescence device. The organic electroluminescence device according to claim 1, wherein the guest material in the light emitting layer is an organometallic complex. The host material in the light emitting layer has the following general formula (2):

[X ¹ in the general formula (2) independently represents N or C-R ² , and at least one X ¹ is N, where R ² is a hydrogen atom and has 1 to 10 carbon atoms. Alkyl group, alkoxy group with 1 to 10 carbon atoms, alkylthio group with 1 to 10 carbon atoms, alkylamino group with 1 to 10 carbon atoms, acyl group with 2 to 10 carbon atoms, aralkyl group with 7 to 20 carbon atoms, substitution Alternatively, it is an unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or an substituted or unsubstituted aromatic heterocyclic group having 3 to 30 carbon atoms.
R ¹ is independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, and 2 carbon atoms. An acyl group of 10 to 10, an aralkyl group having 7 to 20 carbon atoms, an aromatic hydrocarbon group having 6 to 30 substituted or unsubstituted carbon atoms, or an aromatic heterocyclic group having 3 to 30 carbon atoms substituted or unsubstituted. There, adjacent R ¹ may form a ring together,
R ³ is independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, and 2 carbon atoms. An acyl group of 10 to 10, an aralkyl group having 7 to 20 carbon atoms, an aromatic hydrocarbon group having 6 to 30 substituted or unsubstituted carbon atoms, or an aromatic heterocyclic group having 3 to 30 carbon atoms substituted or unsubstituted. is there. ], The organic electroluminescence device according to claim 1 or 2. The organic electroluminescence element according to claim 2, wherein the organometallic complex is a complex in which a planar tetradentate ligand is bonded to a metal having a coordination number of 4. The complex has the following general formula (3):

[M in the general formula (3) is a metal having a coordination number of 4,
R ⁴ , R ⁵ , R ⁶ , and R ⁷ are optionally substituted carbocyclic groups or optionally substituted heterocyclic groups, respectively.
L ¹ is a linking group that connects R ⁴ and R ⁵ .
L ² is a linking group that connects R ⁵ and R ⁶ and
L ³ is a linking group that connects R ⁶ and R ⁷ . ] The organic electroluminescence device according to claim 4, which is a compound represented by. The compounds represented by the general formula (3) have the following structural formulas (3-1) to (3-15):

The organic electroluminescence device according to claim 5, which is any compound represented by. The organic electroluminescence device according to claim 6, wherein the guest material in the light emitting layer is a compound represented by the structural formula (3-1) or (3-3). The organometallic complex has the following structural formula (4-1):

The organic electroluminescence device according to claim 2, which is a compound represented by. A display device comprising the organic electroluminescence device according to any one of claims 1 to 8. A lighting device comprising the organic electroluminescence device according to any one of claims 1 to 8.

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